'use strict';
const EventEmitter = require('events');
const isResumableError = require('./error').isResumableError;
const MongoError = require('mongodb-core').MongoError;
var cursorOptionNames = ['maxAwaitTimeMS', 'collation', 'readPreference'];
const CHANGE_DOMAIN_TYPES = {
COLLECTION: Symbol('Collection'),
DATABASE: Symbol('Database'),
CLUSTER: Symbol('Cluster')
};
/**
* Creates a new Change Stream instance. Normally created using {@link Collection#watch|Collection.watch()}.
* @class ChangeStream
* @since 3.0.0
* @param {(MongoClient|Db|Collection)} changeDomain The domain against which to create the change stream
* @param {Array} pipeline An array of {@link https://www.mongodb.com/docs/manual/reference/operator/aggregation-pipeline/|aggregation pipeline stages} through which to pass change stream documents
* @param {object} [options] Optional settings
* @param {string} [options.fullDocument='default'] Allowed values: ‘default’, ‘updateLookup’. When set to ‘updateLookup’, the change stream will include both a delta describing the changes to the document, as well as a copy of the entire document that was changed from some time after the change occurred.
* @param {number} [options.maxAwaitTimeMS] The maximum amount of time for the server to wait on new documents to satisfy a change stream query
* @param {object} [options.resumeAfter] Specifies the logical starting point for the new change stream. This should be the _id field from a previously returned change stream document.
* @param {number} [options.batchSize] The number of documents to return per batch. See {@link https://www.mongodb.com/docs/manual/reference/command/aggregate|aggregation documentation}.
* @param {object} [options.collation] Specify collation settings for operation. See {@link https://www.mongodb.com/docs/manual/reference/command/aggregate|aggregation documentation}.
* @param {ReadPreference} [options.readPreference] The read preference. Defaults to the read preference of the database or collection. See {@link https://www.mongodb.com/docs/manual/reference/read-preference|read preference documentation}.
* @fires ChangeStream#close
* @fires ChangeStream#change
* @fires ChangeStream#end
* @fires ChangeStream#error
* @return {ChangeStream} a ChangeStream instance.
*/
class ChangeStream extends EventEmitter {
constructor(changeDomain, pipeline, options) {
super();
const Collection = require('./collection');
const Db = require('./db');
const MongoClient = require('./mongo_client');
this.pipeline = pipeline || [];
this.options = options || {};
this.cursorNamespace = undefined;
this.namespace = {};
if (changeDomain instanceof Collection) {
this.type = CHANGE_DOMAIN_TYPES.COLLECTION;
this.topology = changeDomain.s.db.serverConfig;
this.namespace = {
collection: changeDomain.collectionName,
database: changeDomain.s.db.databaseName
};
this.cursorNamespace = `${this.namespace.database}.${this.namespace.collection}`;
} else if (changeDomain instanceof Db) {
this.type = CHANGE_DOMAIN_TYPES.DATABASE;
this.namespace = { collection: '', database: changeDomain.databaseName };
this.cursorNamespace = this.namespace.database;
this.topology = changeDomain.serverConfig;
} else if (changeDomain instanceof MongoClient) {
this.type = CHANGE_DOMAIN_TYPES.CLUSTER;
this.namespace = { collection: '', database: 'admin' };
this.cursorNamespace = this.namespace.database;
this.topology = changeDomain.topology;
} else {
throw new TypeError(
'changeDomain provided to ChangeStream constructor is not an instance of Collection, Db, or MongoClient'
);
}
this.promiseLibrary = changeDomain.s.promiseLibrary;
if (!this.options.readPreference && changeDomain.s.readPreference) {
this.options.readPreference = changeDomain.s.readPreference;
}
// We need to get the operationTime as early as possible
const isMaster = this.topology.lastIsMaster();
if (!isMaster) {
throw new MongoError('Topology does not have an ismaster yet.');
}
this.operationTime = isMaster.operationTime;
// Create contained Change Stream cursor
this.cursor = createChangeStreamCursor(this);
// Listen for any `change` listeners being added to ChangeStream
this.on('newListener', eventName => {
if (eventName === 'change' && this.cursor && this.listenerCount('change') === 0) {
this.cursor.on('data', change =>
processNewChange({ changeStream: this, change, eventEmitter: true })
);
}
});
// Listen for all `change` listeners being removed from ChangeStream
this.on('removeListener', eventName => {
if (eventName === 'change' && this.listenerCount('change') === 0 && this.cursor) {
this.cursor.removeAllListeners('data');
}
});
}
/**
* Check if there is any document still available in the Change Stream
* @function ChangeStream.prototype.hasNext
* @param {ChangeStream~resultCallback} [callback] The result callback.
* @throws {MongoError}
* @return {Promise} returns Promise if no callback passed
*/
hasNext(callback) {
return this.cursor.hasNext(callback);
}
/**
* Get the next available document from the Change Stream, returns null if no more documents are available.
* @function ChangeStream.prototype.next
* @param {ChangeStream~resultCallback} [callback] The result callback.
* @throws {MongoError}
* @return {Promise} returns Promise if no callback passed
*/
next(callback) {
var self = this;
if (this.isClosed()) {
if (callback) return callback(new Error('Change Stream is not open.'), null);
return self.promiseLibrary.reject(new Error('Change Stream is not open.'));
}
return this.cursor
.next()
.then(change => processNewChange({ changeStream: self, change, callback }))
.catch(error => processNewChange({ changeStream: self, error, callback }));
}
/**
* Is the cursor closed
* @method ChangeStream.prototype.isClosed
* @return {boolean}
*/
isClosed() {
if (this.cursor) {
return this.cursor.isClosed();
}
return true;
}
/**
* Close the Change Stream
* @method ChangeStream.prototype.close
* @param {ChangeStream~resultCallback} [callback] The result callback.
* @return {Promise} returns Promise if no callback passed
*/
close(callback) {
if (!this.cursor) {
if (callback) return callback();
return this.promiseLibrary.resolve();
}
// Tidy up the existing cursor
var cursor = this.cursor;
delete this.cursor;
return cursor.close(callback);
}
/**
* This method pulls all the data out of a readable stream, and writes it to the supplied destination, automatically managing the flow so that the destination is not overwhelmed by a fast readable stream.
* @method
* @param {Writable} destination The destination for writing data
* @param {object} [options] {@link https://nodejs.org/api/stream.html#stream_readable_pipe_destination_options|Pipe options}
* @return {null}
*/
pipe(destination, options) {
if (!this.pipeDestinations) {
this.pipeDestinations = [];
}
this.pipeDestinations.push(destination);
return this.cursor.pipe(destination, options);
}
/**
* This method will remove the hooks set up for a previous pipe() call.
* @param {Writable} [destination] The destination for writing data
* @return {null}
*/
unpipe(destination) {
if (this.pipeDestinations && this.pipeDestinations.indexOf(destination) > -1) {
this.pipeDestinations.splice(this.pipeDestinations.indexOf(destination), 1);
}
return this.cursor.unpipe(destination);
}
/**
* Return a modified Readable stream including a possible transform method.
* @method
* @param {object} [options] Optional settings.
* @param {function} [options.transform] A transformation method applied to each document emitted by the stream.
* @return {Cursor}
*/
stream(options) {
this.streamOptions = options;
return this.cursor.stream(options);
}
/**
* This method will cause a stream in flowing mode to stop emitting data events. Any data that becomes available will remain in the internal buffer.
* @return {null}
*/
pause() {
return this.cursor.pause();
}
/**
* This method will cause the readable stream to resume emitting data events.
* @return {null}
*/
resume() {
return this.cursor.resume();
}
}
// Create a new change stream cursor based on self's configuration
var createChangeStreamCursor = function(self) {
if (self.resumeToken) {
self.options.resumeAfter = self.resumeToken;
}
var changeStreamCursor = buildChangeStreamAggregationCommand(self);
/**
* Fired for each new matching change in the specified namespace. Attaching a `change`
* event listener to a Change Stream will switch the stream into flowing mode. Data will
* then be passed as soon as it is available.
*
* @event ChangeStream#change
* @type {object}
*/
if (self.listenerCount('change') > 0) {
changeStreamCursor.on('data', function(change) {
processNewChange({ changeStream: self, change, eventEmitter: true });
});
}
/**
* Change stream close event
*
* @event ChangeStream#close
* @type {null}
*/
changeStreamCursor.on('close', function() {
self.emit('close');
});
/**
* Change stream end event
*
* @event ChangeStream#end
* @type {null}
*/
changeStreamCursor.on('end', function() {
self.emit('end');
});
/**
* Fired when the stream encounters an error.
*
* @event ChangeStream#error
* @type {Error}
*/
changeStreamCursor.on('error', function(error) {
processNewChange({ changeStream: self, error, eventEmitter: true });
});
if (self.pipeDestinations) {
const cursorStream = changeStreamCursor.stream(self.streamOptions);
for (let pipeDestination in self.pipeDestinations) {
cursorStream.pipe(pipeDestination);
}
}
return changeStreamCursor;
};
function getResumeToken(self) {
return self.resumeToken || self.options.resumeAfter;
}
function getStartAtOperationTime(self) {
const isMaster = self.topology.lastIsMaster() || {};
return (
isMaster.maxWireVersion && isMaster.maxWireVersion >= 7 && self.options.startAtOperationTime
);
}
var buildChangeStreamAggregationCommand = function(self) {
const topology = self.topology;
const namespace = self.namespace;
const pipeline = self.pipeline;
const options = self.options;
const cursorNamespace = self.cursorNamespace;
var changeStreamStageOptions = {
fullDocument: options.fullDocument || 'default'
};
const resumeToken = getResumeToken(self);
const startAtOperationTime = getStartAtOperationTime(self);
if (resumeToken) {
changeStreamStageOptions.resumeAfter = resumeToken;
}
if (startAtOperationTime) {
changeStreamStageOptions.startAtOperationTime = startAtOperationTime;
}
// Map cursor options
var cursorOptions = {};
cursorOptionNames.forEach(function(optionName) {
if (options[optionName]) {
cursorOptions[optionName] = options[optionName];
}
});
if (self.type === CHANGE_DOMAIN_TYPES.CLUSTER) {
changeStreamStageOptions.allChangesForCluster = true;
}
var changeStreamPipeline = [{ $changeStream: changeStreamStageOptions }];
changeStreamPipeline = changeStreamPipeline.concat(pipeline);
var command = {
aggregate: self.type === CHANGE_DOMAIN_TYPES.COLLECTION ? namespace.collection : 1,
pipeline: changeStreamPipeline,
readConcern: { level: 'majority' },
cursor: {
batchSize: options.batchSize || 1
}
};
// Create and return the cursor
return topology.cursor(cursorNamespace, command, cursorOptions);
};
// This method performs a basic server selection loop, satisfying the requirements of
// ChangeStream resumability until the new SDAM layer can be used.
const SELECTION_TIMEOUT = 30000;
function waitForTopologyConnected(topology, options, callback) {
setTimeout(() => {
if (options && options.start == null) options.start = process.hrtime();
const start = options.start || process.hrtime();
const timeout = options.timeout || SELECTION_TIMEOUT;
const readPreference = options.readPreference;
if (topology.isConnected({ readPreference })) return callback(null, null);
const hrElapsed = process.hrtime(start);
const elapsed = (hrElapsed[0] * 1e9 + hrElapsed[1]) / 1e6;
if (elapsed > timeout) return callback(new MongoError('Timed out waiting for connection'));
waitForTopologyConnected(topology, options, callback);
}, 3000); // this is an arbitrary wait time to allow SDAM to transition
}
// Handle new change events. This method brings together the routes from the callback, event emitter, and promise ways of using ChangeStream.
function processNewChange(args) {
const changeStream = args.changeStream;
const error = args.error;
const change = args.change;
const callback = args.callback;
const eventEmitter = args.eventEmitter || false;
// If the changeStream is closed, then it should not process a change.
if (changeStream.isClosed()) {
// We do not error in the eventEmitter case.
if (eventEmitter) {
return;
}
const error = new MongoError('ChangeStream is closed');
return typeof callback === 'function'
? callback(error, null)
: changeStream.promiseLibrary.reject(error);
}
const topology = changeStream.topology;
const options = changeStream.cursor.options;
if (error) {
if (isResumableError(error) && !changeStream.attemptingResume) {
changeStream.attemptingResume = true;
if (!(getResumeToken(changeStream) || getStartAtOperationTime(changeStream))) {
const startAtOperationTime = changeStream.cursor.cursorState.operationTime;
changeStream.options = Object.assign({ startAtOperationTime }, changeStream.options);
}
// stop listening to all events from old cursor
['data', 'close', 'end', 'error'].forEach(event =>
changeStream.cursor.removeAllListeners(event)
);
// close internal cursor, ignore errors
changeStream.cursor.close();
// attempt recreating the cursor
if (eventEmitter) {
waitForTopologyConnected(topology, { readPreference: options.readPreference }, err => {
if (err) return changeStream.emit('error', err);
changeStream.cursor = createChangeStreamCursor(changeStream);
});
return;
}
if (callback) {
waitForTopologyConnected(topology, { readPreference: options.readPreference }, err => {
if (err) return callback(err, null);
changeStream.cursor = createChangeStreamCursor(changeStream);
changeStream.next(callback);
});
return;
}
return new Promise((resolve, reject) => {
waitForTopologyConnected(topology, { readPreference: options.readPreference }, err => {
if (err) return reject(err);
resolve();
});
})
.then(() => (changeStream.cursor = createChangeStreamCursor(changeStream)))
.then(() => changeStream.next());
}
if (eventEmitter) return changeStream.emit('error', error);
if (typeof callback === 'function') return callback(error, null);
return changeStream.promiseLibrary.reject(error);
}
changeStream.attemptingResume = false;
// Cache the resume token if it is present. If it is not present return an error.
if (!change || !change._id) {
var noResumeTokenError = new Error(
'A change stream document has been received that lacks a resume token (_id).'
);
if (eventEmitter) return changeStream.emit('error', noResumeTokenError);
if (typeof callback === 'function') return callback(noResumeTokenError, null);
return changeStream.promiseLibrary.reject(noResumeTokenError);
}
changeStream.resumeToken = change._id;
// Return the change
if (eventEmitter) return changeStream.emit('change', change);
if (typeof callback === 'function') return callback(error, change);
return changeStream.promiseLibrary.resolve(change);
}
/**
* The callback format for results
* @callback ChangeStream~resultCallback
* @param {MongoError} error An error instance representing the error during the execution.
* @param {(object|null)} result The result object if the command was executed successfully.
*/
module.exports = ChangeStream;